The earliest developed video images can be seen in documentary film. After the invention of the cathode ray tube (CRT), the commercial television (TV) set was being installed in every house. As the technology advanced, the application of the CRT was extended to the desktop monitor for the computer so that the CRT dominated in the display markets for years. However, one disadvantage of the CRT display is that it emits harmful radiation. In addition, CRT displays typically are large devices due to the internal electron gun. Thus, CRT displays cannot be compact and/or lightweight.
Due to these and other drawbacks, the flat panel display, such as a liquid crystal display (LCD), a field emission display (FED), an organic light emitting diode (OLED), and a plasma display panel, was developed. Among these flat panel displays, the LCD has the advantage of being compact in size and lightweight. Further, LCDs can be made in a variety of sizes, and thus the trend has been to replace the CRT display with the LCD. Further, the LCD can also provide high portability and thus can support wireless communication and network technology.
LCD's can be operated with a thin film transistor (TFT). TFT for use with LCDs can include amorphous silicon LCDs and polycrystalline silicon (polysilicon) LCDs. Recently, a low temperature polysilicon (LTPS)-LCD also has been developed. Because the drive circuit of the LTPS-LCD is located outside the pixel structure, it is important to test whether all devices of the drive work properly.
FIG. 1 is a circuit diagram of the pixel array and the drive circuit in accordance with a conventional drive circuit. As shown in FIG. 1, the drive circuit includes a scan line drive circuit 102 and a data line drive circuit 104. The pixel array 106 includes a plurality of scan lines 108, a plurality of data lines 110 and a pre-charging circuit 112. The scan line drive circuit 102 includes shift registers 114 and 116, a gate 118, and a buffer circuit (not shown). The data line drive circuit 104 includes shift registers 120, 122, and 124, a phase arrangement circuit (PAC) 126, a gate 128 and a horizontal switch 130.
The conventional method of testing a drive circuit will be described with reference to FIG. 1. First, the output terminal of the scan line drive circuit 102 (i.e., the output terminal of the shift register 116) is connected to a pad 132. For the scan line drive circuit 102, the pulse signal 136 is sent to the input terminal of the scan line drive circuit 102 (i.e., the input terminal of the shift register 114). Next, the pad 132 connected to the output terminal of the scan line drive circuit 102 (i.e., the output terminal of the shift register 116) is checked to determine whether there is an output signal. An output signal detected at the pad 132 means that the scan line drive circuit 102 is working properly. However, failure to detect an ouput signal indicates that the scan line drive circuit 102 is damaged. Likewise, the output terminal of the data line drive circuit 104 (i.e., the output terminal of the shift register 124) is connected to a pad 134. For the data line drive circuit 104, the pulse signal 138 is sent to the input terminal of the data line drive circuit 104 (i.e., the input terminal of the shift register 120). Next, the pad 134 connected to the output terminal of the data line drive circuit 104 (i.e., the output terminal of the shift register 124) is checked to determine whether there is an output signal. An output signal is detected at the pad 134, means that the data line drive circuit 104 is working properly. In light of the above, the conventional method for testing the drive circuit has the following drawbacks.
Test results showing that the scan line drive circuit 102 and the data line drive circuit 104 works properly only means that the shift registers 114-116 and 120-124, respectively, work properly. However, this does not guarantee that the other devices of the scan line drive circuit 102 and the data line drive circuit 104 work properly.
Further, test results showing that the scan line drive circuit 102 and the data line drive circuit 104 are damaged do not indicate which of the device(s) of the scan line drive circuit 102 and the data line drive circuit 104 is/are damaged.
Moreover, because the conventional method of testing the drive circuit cannot test all of the devices of the drive circuits, there may be some unknown line defects or point defects that go undetected when testing the pixels.